Method for dewatering of sludge

Abstract

A chemical method is provided for the dewatering of biological sludge that has been digested by a thermophilic digestion process. Five versions of the chemical sludge dewatering method are presented. The primary component in the five versions is a polyquaternary amine, preferably of the di-allyl di-methyl ammonium chloride (DADMAC) variety and from the epichlorohydrin di-methyl amine (epi-DMA) variety. By the first sludge dewatering method, the polyquaternary amine is added directly, along with a polyacrylamide, to the biological sludge. By the second sludge dewatering method, the polyquaternary amine and an anionic polyacrylamide are added separately. By the third sludge dewatering method, a quaternized polyacrylamide, having the polyquaternary amine as part of its polymer chain, is produced by copolymerization of acrylamide with monomers of polyquaternary amine quaternization and is added individually to the sludge. By the fourth sludge dewatering method, the quaternized polyacrylamide from method three is added in concert with a cationic polyacrylamide to the sludge. By the fifth sludge dewatering method, aluminum sulfate, ferric chloride and blends thereof are added, along with polyquaternary amine, as the primary component to the sludge.

What is claimed as invention is: 
     
       1. A method for dewatering biological sludge that has been digested by a thermophilic digestion process comprising: a. adding polymeric quaternary ammonium compounds, aluminum sulfate, ferric chloride and blends thereof, as primary component, to the biological sludge; and   b. adding polyacrylamide to the biological sludge; such that any combinations of the primary component and of the polyacrylamides enhance dewatering of the sludge.   
     
     
       2. The method for dewatering biological sludge according to claim 1, wherein the polymeric quaternary ammonium compounds are from di-allyl di-methyl ammonium chloride (DADMAC) family. 
     
     
       3. The method for dewatering biological sludge according to claim 1, wherein the polymeric quaternary ammonium compounds are from epichlorohydrin di-methyl amine (epi-DMA) family. 
     
     
       4. The method for dewatering biological sludge according to claim 1, wherein the polymeric quaternary ammonium compound, aluminum sulfate, ferric chloride and blends thereof, are added directly to the sludge and, upon formation of microflocs of the sludge from the polymeric quaternary ammonium compound, aluminum sulfate, ferric chloride and blends thereof, a cationic polyacrylamide is added to form a floc that dewaters the sludge. 
     
     
       5. The method for dewatering biological sludge according to claim 1, wherein ratios of the polymeric quaternary ammonium compounds with respect to aluminum sulfate range from about 1:16 to about 1:2 by weight. 
     
     
       6. The method for dewatering biological sludge according to claim 1, wherein ratios of the polymeric quaternary ammonium compounds with respect to ferric chloride range from about 1:8 to about 1:10 by weight. 
     
     
       7. The method for dewatering biological sludge according to claim 1, wherein ratios of the polyacrylamide with respect to aluminum sulfate range from about 1:80 to about 1:8 by weight. 
     
     
       8. The method for dewatering biological sludge according to claim 1, wherein ratios of the polyacrylamide with respect to ferric chloride range from about 1:70 to about 1:7 by weight. 
     
     
       9. The method for dewatering biological sludge according to claim 1, wherein polymer concentration to solids ratio of total polymer dosage requirement in relationship to percentage of solids component of the sludge is between about 50 ppm:1 percent and about 300 ppm:1 percent. 
     
     
       10. The method for dewatering biological sludge according to claim 1, wherein the polymeric quaternary ammonium compound, aluminum sulfate, ferric chloride and blends thereof, are added directly to the sludge, in an amount sufficient to cause formation of a cationic overcharge within a developed microfloc system, and an anionic polyacrylamide is then added for final floc formation. 
     
     
       11. The method for dewatering biological sludge according to claim 10, wherein the polymeric quaternary ammonium compound and the anionic polyacrylamide are in an approximately 1:8 to 20:1 ratio, by weight, with the anionic polyacrylamide having a higher molecular weight than the polymeric quaternary ammonium compound does. 
     
     
       12. The method for dewatering biological sludge according to claim 10, wherein polymer concentration to solids ratio of total polymer dosage requirement in relationship to percentage of solids component of the sludge is between approximately 50 ppm:1 percent and approximately 5000 ppm:1 percent. 
     
     
       13. The method for dewatering biological sludge according to claim 1, wherein the biological sludge is mixed with primary sludge. 
     
     
       14. A composition for dewatering biological sludge according to claim 1 comprising polymeric quaternary ammonium compounds, aluminum sulfate, ferric chloride and blends thereof, as primary component, and polyacrylamide, said components being present in the composition in a ratio to enable the composition to function as an agent for dewatering biological sludge from a thermophilic digestion process. 
     
     
       15. The method for dewatering biological sludge according to claim 1, wherein the polymeric quaternary ammonium compounds, aluminum sulfate, ferric chloride and blends thereof, as well as the polyacrylamide, are used in solution, in emulsion or in dry form.